Characteristic Analysis Of The Symmetric And Asymmetric Structures Of The Boundary Layer Of Typhoon "Likima"

Typhoon Lekima(1909)is selected as an example for numerical simulation,and we choose three moments including twelve o'clock of 7th,twelve o'clock of 8th and eighteen o'clock of 9th in Aug,2009 to represent the development,steady and weakening stages,respectively.The Axisymmetric and Asymmetric structures of boundary layer are analyzed in different stages.The dynamic and thermodynamic structure tendencies of typhoon Lekima boundary layer are diagnosed by using the radial wind,tangential wind,potential temperature and moisture budget equation.The main conclusions are as follows:(1)Comparing the simulation results with the observation data,WRF model can simulate the evolution of typhoon Lekima track,intensity,precipitation and structure greatly.(2)The analysis of the symmetrical structure of the typhoon Lekima boundary shows that tropical cyclone intensity is affected by radii of the strongest radial inflow and maximum wind.In the development and steady stages,the strongest inflow of the boundary layer lies near and inside the radius of maximum wind.The height of dynamic boundary layer is higher than that of thermodynamic boundary layer.The height of the thermodynamic boundary layer at different intensity change stages is between 400 m and 600 m,and their difference is small,same as the height of the thermodynamic boundary layer observed by aircraft(Zhang et al.,2013).(3)The analysis of the asymmetric structure of the typhoon Lekima boundary shows that the asymmetry of the dynamic structure of the boundary layer is much greater than that of the thermodynamic structure.In the development and steady stages,the inflow intensity on the downshear side is greater than that on the upshear side,and the tangential wind speed on the left side of wind shear is greater than that on the right side of wind shear.There are two max tangential wind centers in downshear left quadrant in the steady stage,which is the result of the supergradient wind.In dissipation stage,the radial inflow intensity of the upshear is relatively strong,and the tangential wind intensity on the right side of the shear is relatively stronger and the height of maximum tangential wind is higher on the side close to the land.The maximum tangential wind height on the right side of the shear is greater than that on the left side.(4)Based on budget equations,the result shows that the local budget of radial velocity below 500 m tends to expand from the center to a larger radius from the development stage to steady,weakening stage.In the development stage,the tangential wind tends to be positive within the maximum wind radius;in the steady stage,there is a strong negative tendency of tangential wind near a radius of 30 km because of strong horizontal advection of tangential wind;in the weakening stage,the negative tendency range of tangential wind is larger than that in the first two stages.In the three different stages,the water vapor budget structure is the same as the potential temperature budget structure,but in opposite sign,because the sources and sinks of heat and water vapor are the same.